This invention relates to a fuel injection pump for internal combustion engines having at least one rotating pump piston reciprocating in a cylinder and having a channel which connects the working chamber of the pump with a low pressure chamber and which channel terminates in an outlet opening on the surface of the piston; the amount of opening being controlled by an r.p.m. responsive device having a control edge shiftable axially on the piston. The amount of fuel injected into the engine is thus determined by changing the terminal portion of the fuel delivery during each pressure stroke of the pump piston.
In order to maximize the injection characteristics of the pump relative to the needs of the combustion engine, a relatively large expenditure has hereto been used in achieving this purpose. For example, in a known different type of pump where a channel connecting the working chamber of the pump with a low pressure chamber branches off in the cylinder wall instead of within the pump piston, it is known to enlarge the outlet bore in order to achieve this control of the injection characteristic. However, such an enlargement on the outlet bore of the cylindrical wall is very expensive, since processing tools for this purpose must be introduced into the cylinder.